# Gravitational collapse to a Kerr-Newman black hole

## TL;DR

This paper systematically studies the collapse of rotating, magnetised neutron stars into Kerr-Newman black holes, revealing how initial rotation and magnetic fields influence the black hole's charge and properties.

## Contribution

It presents the first detailed analysis of how rotating, magnetised neutron stars collapse into charged, rotating black holes under realistic astrophysical assumptions.

## Key findings

- Rotating neutron stars acquire a net charge during collapse.
- The resulting black hole is a Kerr-Newman black hole with trapped charge.
- Without rotation or magnetic field, collapse results in Schwarzschild or Kerr black holes.

## Abstract

We present the first systematic study of the gravitational collapse of rotating and magnetised neutron stars to charged and rotating (Kerr-Newman) black holes. In particular, we consider the collapse of magnetised and rotating neutron stars assuming that no pair-creation takes place and that the charge density in the magnetosphere is so low that the stellar exterior can be described as an electrovacuum. Under these assumptions, which are rather reasonable for a pulsar that has crossed the 'death line', we show that when the star is rotating, it acquires a net initial electrical charge, which is then trapped inside the apparent horizon of the newly formed back hole. We analyse a number of different quantities to validate that the black hole produced is indeed a Kerr-Newman one and show that, in the absence of rotation or magnetic field, the end result of the collapse is a Schwarzschild or Kerr black hole, respectively.